When you shop for HVAC, you will see different ratings; but the three most important are the following:
Annual Fuel Utilization Frequency (AFUE) indicates the level of efficiency of gas and oil fired furnaces. A high rating indicates greater efficiency. You should select a furnace with an AFUE of at least 75%. The most efficient furnaces in the market have an efficiency of over 98%.
The Heating Seasonal Performance Factor (HSPF) indicates the energy efficiency of the heat pump. A high HSPF rating indicates that your pump is using less energy and hence is more efficient to run. You should select a heat pump with an HSPF rating of at least 8 and above. The good systems will have energy stars affixed to indicate their efficiency.
Seasonal Energy Efficiency Ratio (SEER) is an indication of the efficiency of the air conditioner and heat pump. The higher the SEER, the less energy the system uses. You should select an air conditioner and heat pump with a SEER of at least 14 with energy stars affixed on the label.